1. Field of the Invention
The present invention relates to a transfer device which mediates communication between first communication devices and a second communication device, a distributed processing system which has the transfer device, the first communication devices and the second communication device, a transfer device control method which controls the transfer device to mediate communication between the first communication devices and the second communication device, and a computer program product embodied for causing a computer to execute the transfer device control method.
2. Description of the Related Art
Conventionally, in a communication system in which communication devices are connected via a network, the communication devices exchange messages mutually so that a notice or demand from one communication device is transmitted to another communication device. And in such a system, a first communication device transmits a command to a second communication device as an operation request causing the second communication device to perform a certain operation, and the second communication device sends back to the first communication device an execution result of the operation as an operation response.
For example, Japanese Laid-Open Patent Application No. 2001-273211 discloses such technology and teaches that a remote processor transmits to a local processor a message which gives a command to be performed by the local processor, and receives a response which indicates a result of the command by the local processor.
In the system of Japanese Laid-Open Patent Application No. 2001-273211, the remote processor is arranged outside the firewall and the local processor is arranged inside the firewall. It is also disclosed that, when needed, the local processor transmits an operation request to the remote processor in the outside of the firewall, and the remote processor transmits a command to the local processor as a response to the operation request. This technology enables transmission of a command to the inside of the firewall from the outside of the firewall.
The technology concerning the above operation request is applicable also to a remote management system which carries out remote control of management operation of a device connected to the communication device.
Japanese Laid-Open Patent Application No. 2002-135858 discloses an example of the application of this technology to a remote management system. In this system, a command from a remote control device having the function of receiving an operation request from a user is transmitted to a remotely controlled device having the function of performing blinding operation and lighting operation, so that a blinding or lighting operation is performed by the remotely controlled device according to the command.
However, there is no teaching in Japanese Laid-Open Patent Application No. 2002-135858 of transmitting a response in respect of the command from the remotely controlled device to the remote control device.
By the way, when exchanging messages between a plurality of communication devices, there is a conceivable case in which one communication device transmits a command to two or more other communication devices. And in such a case, each communication device that receives the command is demanded to return the execution result of the command to the command-transmitting source communication device, respectively.
Conventionally, when performing such operation, the source communication device communicates with the destination communication devices as the destinations of the command individually, and transmits the command to every one of the destination communication devices. Also when receiving a command response, the source communication device communicates individually with each destination communication device to which the command is transmitted, and receives a command response from each destination communication device.
However, according to the conventional system mentioned above, every time a command is transmitted or a command response is received, it is necessary to establish a connection between the source communication device and the destination communication device separately for every destination of the command, respectively. Therefore, the communication overhead becomes large and there is a problem of communication efficiency.
Under the present circumstances, the environment where communication through the network is performed by establishing a dial-up connection still remains, and the above-mentioned problem remains unresolved in such environment. In such environment, a communication fee is charged every time a connection is established, and there is a case in which establishing a connection takes the time of several ten seconds. There is also a problem in that the communication cost increases remarkably as the number of times of establishment of the connection increases.